In free radical polymerizations of fluorinated olefins to form fluoropolymers, it is often desirable to produce polymers that are of lower molecular weight than those obtained where only the initiator and monomer(s) are present. Chain transfer agents are added to lower the average molecular weight of the fluoropolymer obtained. It is often preferred, particularly in fluoroelastomers, that during the chain transfer process an end group is produced which will chain extend or crosslink during curing (crosslinking) of the fluoropolymer. Iodide end groups can undergo chain extension and/or crosslinking, so a process that gives such end groups is desirable.
U.S. Pat. Nos. 4,158,678, 4,234,770 and 4,361,678 describe the polymerization of fluorinated monomers to fluoropolymers in the presence of (cyclo)aliphatic (some containing an olefinic bond) mono- or diiodides which also contain fluorine, and optionally chlorine and/or hydrogen.
U.S. Pat. No. 4,000,356 describes the polymerization of fluorinated monomers to fluoropolymers in the presence of aliphatic (possibly containing an olefinic bond) iodides which also contain fluorine and chlorine and/or hydrogen.
Japanese Patent Application 1-319,512 describes the use of alkyl mono- and diiodides containing 1-3 carbon atoms, such as 1,3-diiodopropane and methylene iodide as chain transfer agents for fluoroelastomer polymerizations.
U.S. Pat. No. 4,948,852 describes the use of mono- or diiodides which are perfluorinated or perfluorochlorocarbons in selected fluoroelastomer polymerizations.
U.S. Pat. Nos. 4,948,853 and 4,983,697 describe the use of alkyl mono- and diiodides in polymerizations to perfluoroelastomers.
No mention is made in the above references of the iodides disclosed herein as chain transfer agents.